Abstract: In order to analyze prehistoric pottery samples, the authors used a X ray dispersal spectral analyser, EDX type 900 HS (Energy Dispersive X-ray Fluorescence (EDX) spectrometry), of high sensitivity and resolution, to highlight the chemical composition of these artefacts. In the paper are presented the results of this experimental research, performed on the batch of ceramic samples from the archaeological site Fetesti-La Schit, Suceava County. In this paper, the authors present the measurements made on some Copper Age ceramics (Cucuteni A and Cucuteni B), using Vickers hardness test to determine the hardness of different types of archaeological ceramics, as physical and mechanical indicator of these artefacts. Porosity, along with other physicochemical and mechanical characteristics, is a feature that can be used in evaluating the quality of archaeological artefacts. The authors propose a number of high techniques for the analysis of this characteristic and present the results of the digital image analysis using specialized software.

The multilayered archaeological site at F etesti -La Schit (figure 1) is known in the archaeological literature for the results of systematic research carried out between 2000-2006, through which important clarifications have been made concerning the vertical and horizontal stratigraphy of the area, the traits of the occupation levels, the characteristics of the constructed and inhabited spaces, the layout and functionality of the archaeological complexes, for all the stages of evolution from this site (Cucuteni A3, Cucuteni Bib, Cucuteni B2a, Horodistea-Erbiceni II, Early Getic Latene, Late Middle Ages)'.

There are three distinct categories of cucutenian pottery (painted, usual and "Cucuteni C"), each with its technological, typological and functional features, very important for the understanding of prehistoric life features of this site.

Among the archaeological remains, pottery is the era of Copper Age largest category of artefacts" For this reason it is a database of sufficient importance that can be studied from several perspectives.

One of the issues of concern related to ceramics is the chemical composition of the material from which they were modelled",

An advanced method to achieve quantitative and qualitative analysis of ceramics can be Roentgen radiation emission spectroscopy. Energy dispersive spectroscopy X -ray radiation (X rays) is an analysis technique used for analysis and chemical characterization of a sample in solid, powder or liquid".

Capability of the method is based on a fundamental principle which says that each chemical element has a unique atomic structure.

On the theory of X-rays production is done in high vacuum tubes containing a heat-emitting cathode and an anode metallic electrons on to download high-energy electrons gained by further accelerating voltage, the tens or hundreds Volts, applied between two electrodes.

So, to stimulate the emission of characteristic X radiation of a sample, a beam loaded with energy, such as electrons or protons, or a cannon X-rays, is directed towards the sample to be analyzed. Photons emitted by the sample are captured by a detector, a semiconductor silicon doped with lithium or SDD detector (silicon drift detector), cooled with liquid nitrogen or by modem Peltier effect. X photons produce a semiconductor ionization, free electron pairs in the electric field polarization effect causes current pulses whose size is proportional to the photon energy. If energy dispersive analysis, X photons of different wavelengths reach the detector, converting it each photon in a pulse of electric charge proportional to the photon energy".

All photons of the same radiation energy, radiation should be represented on the spectrum lines. However, for reasons of imprecision device, they appear as peaks

Some Archaeometrical Determinations on a Lot of Cucutenian Ceramic Materials 9

in the form of a bell (Gaussian profile). The spectrum of X-rays emitted from the sample surface is characteristic of the sample composition, the spectrum analysis and could determine the elemental composition, in the mass concentrations of elements".

Analysis of samples was carried out in the Instrumental Analysis Laboratory within the Food Engineering Faculty Suceava, complex investigation of the samples being made on a spectrometer Shimadzu EDX-900HS (figure 3).

Data processing PC

Silicone drift

Sample chamber

Figure 3. Configuration of EDX-900HS

EDX-900HS Main Unit

With regard to equipment capabilities, spectrometer Shimadzu EDX-900HS is able to detect chemical elements from Na up to U.

The method allows a good separation of the mixture components and a precise identification of existing species.

The quantitative-qualitative analysis results have revealed a relatively uniform composition of chemical compounds with some variations from sample to sample (table 2).

Concentrations of the main metallic oxides are shown in figure 3. It can be seen that the oxides content is different for the studied samples due to the row materials involved and to the specific inorganic pigments used for the colours. Sample SV80 distinguish from the other seven having high Fe203, TiOb K20, P20j contents and a lower Al203 concentration. There is a possibility that this pieces might be from vessel with a different origin and to not be traditional to this archaeological site.

The Vickers hardness test was developed in 1924 by Smith and Sandland. The test evaluates hardness in a manner similar to Brinell taking the ratio between the load applied and the surface area of the resulting impression'. Microindentation hardness is a measurement of the size of a microindentation made by a diamond pyramid -shaped indenter of specified size and shape pressed into a polished surface by a known load. The surface is normally not etched prior to the indentation. The Vickers indenter has four-fold symmetry but makes a deeper indentation and is more inclined to cause fractures in bridle materials than the Knoop indenter what has only two-fold symmetry and is commonly used on ceramics.

Although micro hardness is a widely accepted term, the more accurate name is microindentation hardness. The emphasis on microstructure and microscopic indentation size is largely what distinguishes microindentation hardness from other hardness scales, such as Rockwell and Brinell. Microindentation hardness can he used to measure the hardness of individual grains, very small pieces, and thin layers".

Hardness is not a unique property but a measure of the reaction of the ceramic to the type of disturbing force imposed". In addition to the indentation methods mentioned here, hardness has also been defined in terms of resistance to scratching (e.g. the Mohs scale), plowing, cutting, abrasion, erosion, damping, and rebound (e.g. Shore hardness). There is no definite numerical or even ordinal correspondence between one hardness scale and another.

Microhardness tester is indispensable equipment for metallographic research, product quality control and research and development of new materials. This measurement should be made on a small area without defects, which can provide results with high precision. Most micro hardness testers can perform either Knoop or Vickers hardness tests, only the indenter needs to be changed.

Principle of Vickers hardness test method is forcing an indenter into the sample surface followed by measuring actual surface area of the indentation. Hardness is not

7 R. L. Smith, G. E. Sandland, An Accurate Method of Determining the Hardness of Metals, with Particular Reference to Those of a High Degree of Hardness, in Proceedings of the Institution of Mechanical Engineers, London, 1922 (102), Vol. I (Jan.), p 623-641.

Some Archaeometrical Determinations on a Lot of Cucutenian Ceramic Materials 11

a fundamental property and its value depends on the combination of yield strength, tensile strength and the modulus of elasticity.

indenter

sample

HV = 1,8544 . F d2

Fig. 4. Vickers hardness testing

The composition was made, as we saw, on a Shimadzu EDX-900HS spectrometer and for hardness determination was use a Shimadzu HMV micro hardness tester. This micro hardness tester can work with nine types of loads, belonging interval 98.07mN - 19.61 N. The automatic auto-load eliminates individual variations during loading, giving it a high precision'".

The parameters set for to determine the hardness are action force F of indenter 980 mN and the loading time of 15s. For each sample were made 3 attempts at each hardness in areas that were not influenced by previous attempts.

In order to get good results from the hardness test of the surface preparation of analysis, samples were followed several stages according to the specifications ASTM C 116111. Test results are presented in table 312:

Porosity, which can be considered as secondary "phase" indicates the degree of densification of a ceramic. As a rule of thumb, porosity less than approximately 8% (greater than 92% densified ceramic) means that the pores are discrete, while porosity greater than 8% indicates a continuous network of pores. Porosity measurements by some other methods, such as pycnometry or buoyancy, are sensitive only to open pores and exclude occluded (closed to the surface) pores. Thus, these other porosity methods do not necessarily agree closely with measurements by ceramographic techniques. Porosity decreases strength by two important mechanisms:

• Pores reduce the cross section area of a member.

Some Archaeometrical Determinations on a Lot of Cucutenian Ceramic Materials 13

P . h 13

• ores act as stress-concentratmg note es .

Although several methods are known for determining the porosity 14, for the study of archaeological ceramics porosity from Fetesti-La Schit, we made the analysis in the Materials Science Laboratory of Faculties of Mechanical Engineering, Mechatronics and Management of the "Stefan eel Mare" University of Suceava, using an optical system such as stereo-microscope OPTIKA that has a digital camera QIMAGING Go 3, connected to a PCIS• This system has a 254 pixels/inch resolution that allows jpg image capture with 4915200 pixels size. The total image magnification (stereo-microscope + camera) is 100. For accurate determinations those parameters have been kept to the same level during researches.

Fig. 7. Zone and/or interesting details identification

Fig. 8. Marking the elements of the same type on photography

Each ceramic sample has been photographed on both surfaces (exterior and interior of the ceramic recipient) and in transversal section in representative zones for the sample. The image analysis has been obtained using specialized software, graphic imaging editory program GIMP 2.6.6 (open) and a program for analysis, management and archive of metallographic structures with IQmaterials Media Cybernetics license.

Some Archaeometrical Determinations on a Lot of Cucutenian Ceramic Materials 15

GIMP program is used to simplify some GSA program manoeuvres and to make simple analysis. The photographic images obtained are optical analyzed during which are identified the interest zones.

As an example, in figure 7 has been chosen an area of interest containing a pore. In order to determinate the distribution of porosity surface and its size, and to statistically analyze the measurements, it requires marking this type of detail on sample photography. The easiest method in this case has been offered by GIMP program which helps in pointing out the elements of the same type by marking them on photography (figure 8). Next step regards analysis by established criteria (area, medium diameter, dispersion, etc.). For area calculation it have been applied the GSA program facilities. Due to this purpose the marked detail image is imported in GSA program which sets the analysis criteria. In figure 9 is presented the area analysis chart.

By analysis chart data can be calculated the numerical distribution values, it can be drawn the colour or distribution frequencies histogram, it can be determined the hefts, etc. For example, for percentage distribution calculation can be used the areas estimated in mm' or pixels, applying the same formula: D = VI * 1 OO/V where VI represents the value determined by analysis, and V is the total value, an image characteristic, constant and dependent of the set value for camera resolution. Same calculation can also be made for chart analysis obtained, values easily obtained by GIMP program, by mentioning that, in this case, calculations can only be made to pixel values. We analyzed same two groups of samples from the cucutenian site Fetesti - La Schit and they were called Cucuteni A and Cucuteni B, according to the chronological phase to which they belong. Each sample was analyzed on both surfaces and in section and for each sample was made one sheet. In the following we present one sheet for each group and the final synthesis. Porosity for sample SV61 from Cucuteni A group is presented in figure 10.

Using the porosity evaluation methods we can determine several structural constituents or foreign ingredients from ceramic composition. Examples are given in figures 11 for mineral inclusions, figure 12 for adhesions and figure 13 for deposits.

Calculation area occupied by inclusions, in pixels, for the area leads to:

S =100 . A/At= 288*100/4915200 = 0,0058 %

where: A - inclusions area; At - total area.

High density and compact ceramic, made perhaps using the wheel or rotating equipment. On the exterior side presents decoration in relief of the Cucuteni specific type. On the interior side it has a layer of carbon black colour like edge. Over this layer can be observed are clay like deposits.

Similarly it has been measured the samples porosity from group Cucuteni B, the given example being onto sample SV74 (figure 14-16).

Some Archaeometrical Determinations on a Lot of Cucutenian Ceramic Materials 17

Fig. 14 The general appearance of the outer surface (a) and inside (b) of sample SV74. It is noted that the areas are well finished, clean, relatively small pore inserts minerals, probably sand. The inner surface of the dish was better finished than the outer surface. On the exterior sedimentary limestone deposits can be observed.

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E'

1He:d!e::J-j.:!._~ "1iXeJI!~

~_:li·M: .. 0.-: 1N:rm~r~~ ~.'!-.!

t56:1bNI!J'1'ij) 1J>"Jro(C!!l.~!·ioo.CI

Fig.lS. Identification of porosity on the outer surface of the sample 74 and determine their distribution using the program GIMP. P = 8, 126 % calculated in pixels at a resolution of 2S4 pixels an at an increase order 100.

Our approach is included in the archaeometric research that seeks to multilateral know archaeological ceramics, in this case the Cucuteni culture (Middle AeneolithiciCopper Age), and complement other such concerns 16.

Spectral analysis of samples from the archaeological site from Fetesti-La Schit revealed differences in terms of proportion regarding oxide compounds. These differences may be explained by the choice of different sources of clay for modelling various types of ceramics (pottery incised, painted, usual, "type C") 17. Another possible explanation that should be further investigated is that the vessels from which the samples analyzed were not implemented all the archaeological site has been discovered, but they arrived from the exchange.

Verifying such assumptions would require additional spectral analysis performed and the sources of clay in the archaeological site in question.

Establishing the exact characteristics of the ceramic samples provide a database that can be compared with samples that could be false.

Analysis results suggest that the different kinds of pottery from both phases:

Cucuteni A and B have been obtained using different manufacturing technologies for ceramics. Stages of implementation of product ceramics: selection of the clay, ingredients, modelling, and combustion were outstanding, leading to different values

of hardness, identified by this analysis. Complex study of these samples helps us understand the causes of these values of hardness, setting the ratio between hardness microstructure and composition.

The values obtained for porosity occupies a very wide range, from 0.00292 and 27.606. At least at this stage we can not use this criterion to identify the origin of the samples. Statistical processing of a much larger number of samples may refute this conclusion in the future. Porosity values are highly dependent on raw material quality and processing so that may be used as a criterion for quality assessment. We believe that this criterion could differentiate ceramic materials and crafts areas.

Porosity ranges quite much on the surface. It is a natural phenomenon related to differences between surface roughness inherent to processing and pottery techniques. On the other hand, the section analysis was made in areas unprepared, which greatly influenced the results.

Finally, through further research, we intend to continue archaeometrics investigations for ceramics of the site Fetesti-La Schit, in order to more fully knowing it, in terms of compositional, structural, technological and functional.